Downy mildew overview....causal organisms...its taxonomy....how it starts its infection...downy mildew in grapes and cucurbits like cucumber, bitter gourd, ash gourd etc....its particular causal organism its taxonomy and life cycle....commercial significance...methods to prevent and control the disease...
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Downy mildew in grapes and cucurbits
1. Amrita School Of Agriculture Sciences
(Amrita Vishwa Vidyapeetham)
Arasampalayam(Po), Coimbatore- 642109
DOWNY MILDEW OF GRAPES AND CUCURBITES
2. Downy Mildew are primary
foliage Blights. They attack
and spread rapidly in young,
tender green leaf, twig, and fruit
tissues. They are severe when a
film of water is present on the
plant tissues and the relative
humidity in the air is high
during cool or warm, but not
hot, periods.farmersweekly.co.za
3. SYMPTOMS • Upper & Lower surface of leaf
# Lesions on leaves are
angular, yellowish, sometimes
oily and located between the
veins.
# The upper surface is
showing chlorotic symptoms.
But lower portion with white
patches.
# It requires extra skill to
differentiate this from
deficiencies and other
diseases. Planetnatural.com
4. SYMPTOMS
• Leaves: Infected leaves develop yellowish-green, and
translucent “oily” lesions expand, affected areas turn
brown, necrotic or mottled. The corresponding
lower portion with sporulation of the pathogen, -a
delicate, dense, to grayish, cottony.
• Shoots and Tendrils: Whitish mildew appearance.
The young one are distorted, thickened or curled.
• Fruit: two periods of fruit infection may occur during
a growing season. Shows reduced size, white downy
growth of pathogen.
ohioline.osu.edu
7. Downy Mildew of Grapes
Occurrence
# The disease is known to occur under humid conditions.
# In Europe and in eastern half of U.S.A , Asia, Australia, South
America.
# In India the diseases is Maharashtra and Karnataka.
# Downy mildew is a highly destructive disease of grapevines in all
grape growing areas of the world where there is spring and summer
rainfall at temperatures above 10 degree celsius.
# It affects the leaves, fruits and vine.
# Losses through necrosis of leaf tissue and defoliation . Dwarfing
and killing of leaves takes place.
# The symptom expression starts from 5 to 7 days.
9. Characterisics of P. viticola
• Mycelium: Aseptate and hyaline.
• The pathogen is obligate parasite.
• Zoospore and oospore are
biflagellate.
• They are recently proved to be
heterothallic.
• ‘Lemon’ shaped special sporangia
confirms the presence of P. viticola
revolvy.com
revolvy.com
22. Control
• Proper drainage.
• Sanitation: Removal of old leaves.
• Pruning: Prune the infected shoots.
• Cultivars: ‘Cascade’, ‘Chelois’, ‘Concord’, ‘Foch(Marechal Foch),’
‘Himrod’ and ‘Stueben’ are the most resistant varieties.
23. Reference
• George N. Agrios, Plant Pathology, 2005, Elsevier Academic Press.
• D. Alice, C. Jeyalakhmi, A.S Krishnamoorthy, M. Karthikeyan,
Fundamentals Of Plant Pathology, 2017,Sri Sakthi Promotional Litho
Processes publications,
• Dr. G. Arjunan, Dr. D. Dinakaran, Dr. S. Parthasarathy, Diseases Of
Horticultural Crops.
• American Phytopathological Society website
https://www.apsnet.org/
